Acetylcholine (Ach) is the principal transmitter of the parasympathetic nervous system. The physiological actions of Ach are mediated by activation of either nicotinic or muscarinic receptors. Both of these receptor classes are heterogeneous: e.g., the muscarinic receptor family comprises five subtypes (M1, M2, M3, M4, and M5) each encoded by distinct genes and possessing unique pharmacology and distribution.
Almost all smooth muscle tissues express both muscarinic M2 and M3 receptors, both of which have a functional role. M2 receptors outnumber M3 receptors by a proportion of approximately 4 to 1. Generally, M3 receptors mediate the direct contractile effects of acetylcholine in the vast majority of smooth muscle tissues. M2 receptors, on the other hand, cause smooth muscle contraction indirectly by inhibiting sympathetically (β-adrenoreceptor)-mediated relaxation.
Compounds that act as antagonists of muscarinic receptors have been used to treat several disease states associated with improper smooth muscle function. Until recently, most of these compounds have been non-selective for the various muscarinic receptor subtypes, leading to unpleasant anti-cholinergic side-effects such as dry mouth, constipation, blurred vision, or tachycardia. The most common of these side-effects is dry-mouth resulting from muscarinic receptor blockade in the salivary gland. Recently developed M2 or M3 specific antagonists have been shown to have reduced side effects. Evidence suggests that concurrent blockade of M2 and M3 receptors could be therapeutically effective in the treatment of disease states associated with smooth muscle disorders.
Few M2/M3 selective antagonists have been developed. The present invention fills this need by providing these types of antagonists useful in the treatment of disease states associated with improper smooth muscle function.